Polymer and Hydrogen Bonds

Experimental Design

After reading each procedure write down the problem, hypotheses, input variable or variables, possible dependent variables, parameters and the treatment. The experiments are essentially tests in which the input variable is not changing, so you only need to describe one treatment for each experiment. Notice the hints below.

Problem: The problem is a question that you will attempt to answer by experimentation. (Example: What will happen if polyvinyl alcohol is combined with borax?)

Hypotheses: A hypothesis is a prediction that can be tested experimentally. There is no reason to only have one hypothesis. Good experiments often have several hypotheses. (Examples: 1) Combining polyvinyl alcohol and borax will produce a new substance that is very plastic. 2) Combining alcohol and borax will produce a new substance that is not plastic but very elastic. 3) Combining alcohol and borax will release heat to the surrounding environment. 4) Combining alcohol and borax will absorb heat from the surrounding environment.)

Input Variable: This is the "thing" that you, the experimentor, are changing. (Example: If the experimentor is interested in looking at the effect of the concentration of a reactant on the progress of a chemical reaction, then the input variable would be the concentration of a reactant .) Many good experiments only have one input variable. (Example: You are to investigate the problem: What is the effect of temperature on the rate of the reaction that combines alcohol and borax? An experiment designed to investigate this problem would have the input variable, temperature .) If you, the experimentor, were interested in changing the concentration of two reactants, then your experiment would have two input variables. You would therefore be interested in a possible interaction between the two input variables. In all of the experiments in this activity the input variables are the reactants and the known properties of the reactants for each procedure.

Dependent Variable: This is the "thing" that changes as a result of a change in the input variable. (For example: if known reactants are combined to produce an unknown product, the dependent variables would be all of your observations concerning the physical properties of the unknown product.) Physical properties of solids can include plasticity, elasticity, flexibility, hardness, texture, density, thermal conductivity, electrical conductivity, transparency, and the very important property, color. Physical properties of liquids include: plasticity, viscosity, color, transparency and density. Physical properties of gases include density, color, and odor. In all of the experiments of this activity the dependent variables are your observations once you mix your reactants.

Parameters: Parameters include all of the "things" that you, the experimentor, do not want to change while changing the input variable. (Example: If you, the experimentor, are only interested in changing the temperature while doing a chemical reaction, then you would not want to change the intitial concentrations or amounts of your reactants. Nor would you want to change any other environmental factor that may influence the chemical reaction, such as light and air pressure. When reporting the results of your experiment you should always specify the conditions, i.e., the parameters, so that your experiment is reproducible. In all of the experiments in this activity the parameters include the safety precautions, your method for how you will make your observations, and the amount of times that you will be observing each reaction.

Treatments: A treatment is the description of what you, the experimentor, do each time you vary the input variable. It is often described by simply specifying the level of your input variable. (Example: Four treatments were designed to determine the effect of temperature on a chemical reaction: treatment one was 10 degrees C, treatment two was 20 degrees C, treatment 3 was 30 degrees C, and treatment four was 40 degrees C.) In all of the experiments in this activity the single treatment can be described by writing down the volume and concentration of each reactant.

Control: This is a term for a treatment that is designed to be a basis of comparison. Typically, a control will not have any amount of an input variable, though in the case of temperature, your control treatment would probably be the treatment with the lowest temperature. (Example: If you want to do an experiment to test the effect of a drug on AIDS, a control would be a pill called a placebo, that looks like the drug, tastes like the drug, but does not contain the drug.)

Replications: This is the number of times you repeat all of the treatments. An experiment in which each treatment is done three times has three replications.

Be sure to also write down a data table to record all of your observations. I suggest making a separate row for the properties of each reactant, i.e. input variables, and a separate row for each dependent variable. Be sure to make the boxes in your tables big enough to describe detailed observations.